This invention relates to devices which detect and/or treat tachyarrhythmias (rapid heart rhythms), and more specifically, to mechanisms to distinguish among various tachyarrhythmias and to provide therapies to treat the identified tachyarrhythmias.
In conjunction with implantable cardioverters and defibrillators, numerous mechanisms for communication between the patient and the implanted device have been proposed. Particularly in conjunction with implantable defibrillators or cardioverters, the provision of a patient warning signal indicating that cardioversion or defibrillation is about to commence, is disclosed in U.S. Pat. No. 4,210,149 issued to Heilman et al, U.S. Pat. No. 5,332,400 issued to Alferness and U.S. Pat. No. 5,190,034 issued to Sholder. The warning signals provided to the patient typically take the form of audio signals or electrical stimulation using electrodes associated with the implanted device.
In addition to communication from the implanted device to the patient, communication and control signals from the patient to the device are also known to the art. For example, U.S. Pat. No. 5,443,486 issued to Hrdlicka et al and U.S. Pat. No. 4,365,633 issued to Loughman et al, both disclose devices allowing the patient to program or control the operation of the implanted device. Particularly in conjunction with implanted defibrillators, the warning and control functions have been integrated, so that the patient is provided with a warning signal prior to defibrillation or cardioversion, and with a mechanism for overriding the implanted device, to prevent delivery of an undesired or unneeded cardioversion or defibrillation pulse. Such systems are disclosed in U.S. Pat. No. 5,190,034 issued to Sholder and U.S. Pat. No. 4,210,149 issued to Heilman et al, cited above. In such systems, the implanted device monitors the patient's heart rhythm to determine the presence of an arrhythmia requiring cardioversion or defibrillation. Having detected such a rhythm, the device provides the warning signal indicating the imminent delivery of a cardioversion or defibrillation shock, which the patient may then override. Allowing the patient to initiate delivery of a cardioversion or defibrillation shock is also known to the art. For example, U.S. Pat. No. 3,952,750 issued to Mirowski et al discloses atrial implantable cardioverter in which the patient initiates delivery of an atrial cardioversion pulse, and U.S. Pat. No. 5,498,062 issued to Adams et al discloses an implantable defibrillator in which the patient initiates operation of the arrhythmia detection mechanism, to determine whether delivery of a cardioversion or defibrillation pulse is necessary.
Presently available implantable anti-arrhythmia devices employ sophisticated arrhythmia detection and classification methods to accurately determine whether delivery of therapy is needed. Particularly in the context of devices such as cardioverters and defibrillators which have the potential to induce arrhythmias if not properly synchronized to the patient's heart rhythm, these detection methods tend to be conservative, in order to avoid delivery of unnecessary therapy. In such cases, it may sometimes take the implanted device longer than the patient to determine that delivery of a therapy is needed. Patient activators as discussed above which trigger therapy on request address this problem, but do not provide for the possibility of patient error. The device described in the Adams patent cited above deals with the possibility of patient error by determining whether therapy is warranted after a request by the patient, but employs the same set of criteria for patient requested therapy as for device initiated therapy, and thus may not provide for therapies as quickly or as often as may be desirable in response to patient's requests. The present invention is believed to offer the patient the ability to quickly and safely receive therapy in response to a request, when warranted.
In the context of a patient activated implantable atrial defibrillator, there is often some lag time between the patient requesting the delivery of therapy and the actual delivery of therapy. In the context of a device as in the Adams '062 patent, in which arrhythmia detection is initiated in response to the patient's request for therapy, there is a substantial lag time associated with the detection of algorithm. Even in systems such as disclosed in the Mirowski '750 patent described above, a request for therapy initiates charging of the output capacitors, which can take some time. Assuming some requirement of synchronization to the ventricular rhythm is provided in the device, the process of synchronization may take additional time. Thus, there is a variable waiting period following a patient's request for therapy. Because atrial cardioversion is painful for some patients at energy levels sufficient to terminate their atrial fibrillation, it may be beneficial to the patient to allow the patient to prepare himself or herself to receive the shock, which in turn may allow the patient to tolerate a higher energy level shock. However, to the extent that the waiting interval between the request for therapy and the delivery of therapy is variable, the patient's ability to brace for the shock is correspondingly diminished.